An apparatus of this type, known from DE-A-4,216,729, and its counterpart U.S. Pat. No. 5,359,408 is designed as a test chamber, within which are arranged surface or image sensors formed by CCD cameras. During the examination, the bobbin to be examined rests on a stand and is illuminated in a floodlight manner by two light sources. As can be taken from DE-A-4,112,073, and its counterpart U.S. Pat. No. 5,289,983 the test chamber is arranged centrally for an entire spinning mill in the region of an intermediate store. This means that the bobbin testing takes place at a moment when an inadequate winding quality can no longer be corrected, but the particular bobbin has to be separated out as a reject. Apart from that, with this known apparatus, only the state of the outermost thread layer of the bobbin can be checked, and no evidence relating to the winding quality inside the bobbin is possible. Consequently, the possibility cannot be excluded, and it is even probable, that yarn bobbins judged to be good by this apparatus may have a poor winding quality.